1. Field of the Invention
The present invention relates to an image capturing apparatus, an image capturing method, and a storage medium.
2. Description of the Related Art
Currently, various ophthalmic apparatuses using optical apparatuses are known. For example, various apparatuses such as an anterior ocular segment image capturing apparatus, fundus camera, and SLO (Scanning Laser Ophthalmoscope) are used as apparatuses for the observation of the eyes. Among these apparatuses, an optical coherence tomography apparatus based on OCT (Optical Coherence Tomography) using multiwavelength light wave coherence can obtain a tomographic image of a sample at high resolution. The optical coherence tomography apparatus is therefore becoming indispensable to outpatient clinics specialized in retinas as an ophthalmic apparatus.
An optical coherence tomography apparatus (to be referred to as an “OCT apparatus” hereinafter) irradiates an object to be examined with measurement light which is low-coherent light, and can perform high-sensitivity measurement of backscattered light from the object by using a coherent system or coherent optical system. Low-coherent light has the property of being able to obtain a high-resolution tomographic image by increasing the wavelength width. In addition, the OCT apparatus can obtain a high-resolution tomographic image by scanning measurement light on an object to be examined. Therefore, the OCT apparatus can obtain a tomographic image of the retina at the fundus of an eye to be examined as an object to be examined, and hence has been widely used for ophthalmic care and the like for the retina.
On the other hand, the OCT apparatus is generally equipped with optical systems for fundus observation, anterior eye observation, and the like to implement alignment adjustment between the apparatus and an eye to be examined. In order to use the OCT apparatus together with these optical systems, the apparatus is configured to use light sources of different wavelengths for the respective optical systems and perform optical path separation depending on the wavelengths by performing wavelength separation using an optical path branching unit such as a dichroic mirror. The tomographic image acquired by the OCT apparatus will undergo the correction processing of restoring the phase shifted by the dispersion of light for each wavelength in consideration of the dispersion of light at the measurement optical unit and the reference optical unit. For example, according to Japanese Patent Laid-Open No. 2010-12111, dispersion correction is performed by calculating a phase shift amount based on a fundus tomographic image.
Increasing the accuracy of wavelength separation by the dichroic mirror which is the optical path branching unit described above will increase the number of films of the dichroic mirror. This makes the dichroic mirror have phase characteristics showing arbitrary curves (different phase characteristics) in accordance with the wavelengths of light. The different phase characteristics include a phase characteristic which can be corrected in consideration of dispersion and an irregular phase characteristic which cannot be corrected even in consideration of dispersion. With regard to irregular phase characteristics, it is impossible to correct an OCT image by the above correction processing with consideration to dispersion. This can cause the problem that the OCT image (the tomographic image of the object to be examined) blurs in the optical axis direction. It is preferable to acquire a tomographic image of the object with high accuracy even if the phase characteristics of interference light include a phase characteristic which can be corrected in consideration of dispersion and an irregular phase characteristic which cannot be corrected even in consideration of dispersion.
In consideration of the related art, the present invention provides an imaging technique which can acquire a tomographic image of an object to be examined with high accuracy even if the phase characteristics of interference light include a phase characteristic which can be corrected in consideration of dispersion and an irregular phase characteristic which cannot be corrected even in consideration of dispersion.